"The transformer is an integral part of modern electrical power systems. In short, its function is to convert low-current, high-voltage electricity into high-current, low-voltage electricity (or vice versa) with virtually no energy loss." (Coltman, 1988) Transformer selection is an important factor in energy efficiency. Transformers play an important role in the electricity distribution system and account for a large part of energy consumption. Therefore, if the choice of transformer is not made correctly, it can have negative consequences in terms of energy efficiency and economics.

In terms of energy efficiency, the two main factors in transformer selection are load factor and transformer efficiency. Load factor is the ratio between the actual power of a transformer and its rated power. When the transformer operates at a load lower than its rated power, its efficiency may decrease. Therefore, the selection of the transformer should be done by considering the load factor. In addition, transformer efficiency is also important in terms of energy efficiency. The efficiency of the transformer is the ratio of transformer losses to total power. A higher efficiency means less energy loss and less energy consumption. Therefore, in terms of energy efficiency, higher efficiency transformers should be preferred. In 1999, Turkish Electricity Transmission Corporation (TEDAŞ) published Tedaş-Mlz/99-032.E. technical specification for Hermetic type MV/LV distribution power transformers (A Plus Transformer), thus ensuring that the transformers to be used throughout the country are highly efficient.